Centralized traffic controlling system for railroads



'l Fla. 1.

June 30, 1936. w. D. HAlLl-:s 2,045,908

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed 0G13. 5l', 1934 BY ATroRN'EY 30, 1936, w. D. HAlLEs CN'TRALLZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed Oct. 3l, 1954 5 Sheets-Sheet 5 June 30, 1936.

w. D. HAILES CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS 5 sheds-sheet 4 Filed dot. 31', I1934 ATTORNEY Patented June 30, 1936 UNTED STATES CENTRALIZED TRAFFHC CONTROLLING SYSTEM FOR RAILROADS William D. nenes, Brighton, N. Y., assignor to General Railway Signal Company, Rochester,

Application October 3l, 1934, Serial No. 750,828

14 claims.

. This invention relates to centralized traffic controlling systems for railroads, and more particularly pertains to the use of transmission lines in the communication part of such systems.

5y A centralized trafiic controlling system for railroads usually places a central office in communication with a large number of outlying eld stations in such a Way that controls may be transmitted to these i'leld stations for the governing of the operation of traffic controlling devices located at the several stations, and also, for the transmission of indications from the station to thev central oiiice to advise the operator of the location of trains and the condition of the traiilicV controlling devices.

In such a system, irrespective of Whether it is of the direct Wire type or of the selector type, it is usually preferable to provide the source of energy for the transmission line circuits at the central oiice, as the battery source, or other current supply, can then be maintained with greater efciency and accuracy. With this arrangement of current supply, it usually occurs both in direct Wire type systems and in selector type` systems that there are diiiiculties to be overcome because of the inherent inductive and capacitive characteristics of a relatively long transmission line extending from the central cnice to the outlying eld stations.

The present invention proposes to so associate communication systems of the above described character with their line circuits as vto overcome the diiliculties encountered.

In one situation, it is desired to have a transmission line extending from a central oiiice to an outlying eld station, or stations,4 Which completes a circuit for a source of energy and aY relay in the central oice in such a `manner that this circuit is controlled by an open or closed contact at the outlying field station. With this arrangement, it usually occurs both in direct Wire type systems and in selector type systems that the sequence ofv events is such that the ldistributed capacity of the transmission line connecting the controloce With the field station becomes discharged, so that the application of energy at the central ofce results in a temporary surgefof current which is conveniently termed the charging current. A charging current flows irrespective of Whether the line circuit is 'opened' orclosed at the field station from which an indication is to be received.

It has been found that in some instances the charging current that flows into an f open Y circuited line reaches a peak value considerably greater than the current that normally flows under the steady" Conductive conditions of the lineV circuit and that this charging current surge lasts forv an appreciable length of time. Under these conditions a relay inserted inthe line, for the purpose detecting the closedconductive condition of the line, has been undesirably picked up by the 5 charging current when it was supposedv to remain in the released position in accordance with the open circuit condition of the line.`

The present invention proposes to provide means in cases of this type wherein the trans-,10 mission line may be charged, prior to the insertion of the indication receiving relay at the central olice into the transmission line circuit connecting the centraloiiice With the eld apparatus.

Other objects, purposes and characteristic fea- 15 tures of the present invention will be in part obvious from the accompanyingy drawings, and in part pointed out, as the description of the invention progresses.

In describing the invention in detail, reference 20V Fig. 1 illustrates ina diagrammatic and conven- 25 tional manner the embodiment of the present invention in a direct Wire type of indicating systems; and- Fig. 2 illustrates in a diagrammatic and conventional manner the application of the present in- 30 vention to the line circuits of a selector type communication system, as disclosed, for example, in the pending application of Judge et al, Ser. No. 640,062, led October 28, 1932.

Figs. 3 and 4 illustrate in a diagrammatic and 35 conventional manner parts of the control oiiice apparatus in a selector type communication system as disclosed, for example, in the pendingV application of Judge et al., Ser. No. 640,062, filed October 28, 1932; Y

Fig. 5 illustrates in a diagrammatic and. conventional manner parts of a field station in a selector type communication system as disclosed, for example, in the pending application of Judge et al., Ser. No., 640,062, filed October 28, 1932.

l For the purpose. of simplifying the illustration and facilitating in the explanation, the various parts'and circuits constituting the embodiment of the invention have been shown diagrammatically and certain conventional illustrations have been 50 employed, the drawings having been made more With the purpose of making it easy to understand the principles and mode of operation, than with the idea of illustratingY the specific construction and arrangementof parts that Would be employed 55 '..to the control office,

in practice. Thus, the various relays and their contacts are illustrated in a conventional manner, and symbols are used to indicate connections to the terminals of batteries, or other sources of electric current, instead of showing all of the wiring connections to these terminals.

The symbols (-1-) and are employed to indicate the positive Yand negative terminals respectively of suitable batteries, or other sources of direct current; and the circuits with which these symbols are used., always have current flowing in the same direction. When alternating current is used in place of direct current, the particular symbols employed represent the relative instantaneous polarities.

For the purpose oi disclosing the present invention, it has been shown appliedto a unit direct wire system in Fig. 1 and toa selector type of system in Fig. 2. As the particular advantages of the present invention will be best understood' by a description of both types of systems, a detailed description of Figs. l and2 will be given separately.

Unit wire system In aunit wire system, (see Fig. 1) each device to be indicated in the central control oiiice is usually provided with a separate circuit. This may be accomplished by providing an individual wire for each device with a common return wire for all devices. On the other hand, individual line circuits may beprovided for each device to be indicated. In either case, the application of the present invention isthe same.

As one embodiment of. the present invention, a section of track TK having the usual closed circuit type of track circuit with a track relay T and a track battery 4 has been shown as having its occupied or unoccupied condition transmitted Connecting the field station at which the track relay T is located, and the control ofce are two line wires I3 and I5 of a suitable transmission" line. These line wires I3 and I5 form a circuit which is supplied with .current from a line battery I8 located in the cen- Y contact 'I may be of the make-before-break type,

if desired, so as to shift the line circuit from a charging resistor CR to the lower winding of a message receiving relay ME without allowing a momentary open circuit condition during which a precharge might leak off due to line leakage, as later explained in detail. A

'Ihe impulsing relay IE is controlled by a manually operable self-restoring push button K. Another manuallyoperable self-restoring push button CK is employed to cancel a message or indi. cation previouslyreceived by the message receiving relay ME by opening its` stick circuit.

An indication lamp I is associated with the message receiving relay ME to display to the operator the particular condition of the outlying track relay to be indicated, although it is to be under- "stood that any other type of. indicating means might be employed and still be within the contemplated scope of the present invention.

It is believed expedient to point out the sequence of operations, and operating features in connection with Fig. l at this time. However, the electrical characteristics of Figs. l and 2 will be considered together.

Operation of Fig. 1.--With the system in its normal condition, as illustrated, and the track section TK unoccupied, the track relay T is normally energized as in all normally closed circuit type of track circuits. Assuming that this unoccupied condition of the tracksection TX existed upon the last action of the operator` to ascertain theY condition of the track section, the indication the control office are deenergized.

Let us assume that the operator desires to ascertain or check the condition of the track section TK while itv is still unoccupied. To do this, he actuates the key K to a depressed position which applies energy tothe impulsing relay IE by a circuit apparent from the drawing. The response of the contact 6 of relay IE connects the positive terminal of the battery source I8 to the line wire i5 through front contact 6, back contact 'l of relay ZE, charging resistor CR, to the line wire I5. Thus, the line wires I3 Vand I5 are connected to their respective terminals of the battery I8, but a conductive circuit is not completed by reason of. the open condition of back contact I'I of the track relay T.

Assuming that the back contact I'I of the track relay T has been closed subsequent to the last energization of the line circuit, then any charge which may have been stored in the distributed capacity of the transmission line has been dissipated, so that the application of the terminals of the battery source I8 to the transmission line causes a charging current to flow until the distributed capacity of the transmission line is substantially charged by the potential of the battery.

It is noted that this charging current flows through the charging resistor CR. which is preferably of the non-inductive type. The resistance value of this resistor CR is preferably such as to permit the distributed capacity of the line circuit to be suiiiciently'charged within the desired time, and still have sufficient resistance to prevent excessive current flow in case the line circuit should have a short circuit or was conductively closed by the back contact II of the track relay T. The relation of the charging resistor CR to the charging current and the time at which the impulsing relay 2E may be shifted to include the relay ME in the line circuit will be considered more in detail hereinafter.

'Ihe closure of front contact 5 of the impulsing relay IE energizes the impulse repeatingrelay 2E by a circuit obvious from the drawings. 'I'his imin the line circuit.

When the distributed capacity of the transmission lineV is substantially charged, there is sub- 75 stantially no current flowr when thecontact 'I shifts the line circuit, to include the lower winding of the relay ME'` As they line circuit is; con-- ductively open due to the open condition of back r Contact I'I of the track relay T; the relay. ME

remains deenergized and the. indicator lamp I remains unilluminated advising the operator or the unoccupied condition of the. track. section The momentary actuation of the key K by thevv operator is usually sufficient to cause the succes.- sive energization of the relays IE and 2E as. the charging oi the transmission line and the inclusion of the relay ME occur in such rapid sequence. Should the timing characteristics ofthe combination involved be such as to require a longer time period, then the relay IE can be made-extremely quick in picking up but muchslower in releasing,

so that its releasing period will be of szuiiicient duration fory the picking up of relay 2E and the charging of the line circuit.

Now let us assume that the track relay T is de.-

energized with its back contact II closed. Then upon the closure ofI the front contact 6 of the relay IE following the, manual actuation of the key K, the transmission line is energized through the charging resistor CR.. Upon the pic-king up of the contact 'I ofv the impulse repeating relay 2E, the lower winding of the relay ME is. included in the circuit. With the back Contact Il of the track relay T closed, the current flow is of a valueabove the pick up value of the relay ME duringv the time that the contacts l and 'I are picked up, which causes the' contacts of the relay ME to be actuated to energized positions.

With the contacts of the relay ME picked up, a stick circuit is closed from through a circuit including the front point of the manually operable cancelling key CK, front contact I I' of the relay ME, upper winding of the relay ME, to This stick circuit maintains the relay ME energized dependent upon the actuation of the cancelling key CK. Under such conditions, the indicator lamp I is energized through front Contact 9 of the relay ME so long as this stick circuit is closed, irrespective of the fact that in the meantime the. back contact iI of the track relay T mayl again open. It is. of course obvious, that relays IE and 2E sequentially release following the release of the key K` after having accomplished f their allotted functions.

Should the operator desire to ascertain the condition of the track section TK following the reception of an occupied indication, he first actuates the. cancelling key CK, which deenergized the stick circuit of the relay ME to extinguish the indicator lamp I, and then actuates the manually operable key K to allow the indicator lamp I to be controlled in accordance with the occupied or uhoccupied condition of the track section TK, as above described.

It should be noted, that the distributed capacity between the line wires I3 and I may-be dis,- charged due to two reasons, namely, the closure off back contact Il of the track relay T while the, terminals of the battery I8 are removed from the two line wires I3 andl I5, or due to the leakage of the charge from the wires during av protracted period of deenergization of the line circuit although the back contact Il of the track relay T is open.

Selector type system (See Fig. 2)

The linecircuitsv of a selector type system,l such as, disclosed inthe pendingV application ofv Judge et. al, Ser.. No. (#103062, filed October 28 1.932` have been shown in Fig. 2 with the present invention applied t-l'iereto- This application of Judge'et al is the b asis and corresponds to the disclosure of they British Patent No'. L119,399, dated October 28,

1932, and filed under the provisions of the. International Convention, to which reference may be made for details of operation of the system, although itis believed that the understanding of the invention and thev system with which it is associated may be readily obtained in` connection with the drawings ci the present application and the description in connection therewith. All of the parts mentioned in the present application which correspond to the disclosure of such prior application of Judge et al, and the correspondingr British patent, have the same reference characters; so as to provide; ready identication of such corresponding parts.

In a systemof this character,l the field stations and control cnice are interconnected by four line wires Il), I2, Ii and I6. The line wires Ill and I2 are connected together at the last field station in the system and are energized with positive and negative impulses from a control battery CB in the control oilice for the purpose of transmitting the controls and for the purpose of causing the synchronous step-by-step operation at the control ciiice and at the several eld stations.

At the control chica a series, of' stepping relays. IV, 2V, 3V and LV together with a half-step relay VP (see Fig. ll)l operate step-by-step in response to the time spaced impulses impressed on the line cir. cuit. Likewise, at the eld station a series of step.- ping relays IVI, ZV1, 3V1 and LV1 together with a half-step relay VP1 (see` Eig. 5.) operate the stepby-step! inY response to the time spaced Vimpulses impressed upon the line circuit.

The l-ine wire lil.y includes a three-position polar remy F (with sultan@ expo-nenn at the control office, and at each iield station, which repeats the imp-ulses of each-series. The particular polarity ofthe impulses of ,each series pla-,ced upon the control and stepping circuit is determined by polarity selecting relays PCand NC which determine respectively whether the impulses are positiveor negative in character. These relays PC and NC are operated in accordance with the station code calls. and the controls to be transmitted, as show-n in. Fig. 3f of the accompanying drawings, so'th-at one or the otherr of these relays is energized for each step taken by: the stepping relays in the control ciliceL The duration of each impulse of a series. as well as the time spaces between such impulses is determined in accordance with the operation of an impulsing' relay EP and its controlling relay E which is operated in response to the operation of the stepping relays IV, 2V, 3V

and LV together with the half-step relay VP (see Fig. 4a) n At the control oii'ice, each-impulse is repeated by the relay F, but irrespective of the! polarity of such impulse, itis also repeated by a line repeat- Ying that the relay SA is slow in picking up. upon the first, impulse of each series but is relatively much, slower in dropping away so as to maintain its point contacts closed during the time spaces.

between impulses in each series of impulses. The relay SA is also provided with a repeater relay 2SA.

Similar relays are provided'at each of the field stations, but for convenience, only the relays F1,

FP1, SA1, and SB1 have been shown at o-ne eld station which is typical of all eld stations.

The relay 2FP in the control ofce directly operates the stepping relays IV, 2V, 3V and LV to take one step for each deenergization of` the line circuit and to cause the relay VP to operate to an opposite position for each energization of the line circuit. It will be apparent that this operation is dependent upon the picking up of the relay SA which occurs on the rst impulse of a cycle of operation and is maintained throughout such cycle of operation so that the stepping relays may be stuck up until the end of such cycle. At the eld station, similar operation occurs, but the stepping relays are operated directly from the relay FP1 dependent upon the picking up of the relay SB1 and the closure of a front contact I34 of the station selecting relay S01 or front contact I'II of the lockout relay L01. These station Yrelays will be mentioned more in detail hereinafter.

In'Fig. 3, a cycle controlling relay C is shown as controlled by a starting button ISB, that is, each time the button ISB is actuated, picking up a code determining relay ICD, the pick up circuit for the cycle controlling relay C is closed so as to cause the system to transmit controls,

all of Which has been disclosed in detail in the i above mentioned prior application. The cycle controlling relay C when picked up together with the code determining relay ICD renders the relays PC. and NC over buses 41 and 48 subject to the code jumpers 58, 55 and 40 and the control lever SML successively on the steps marked off by the stepping relays IV, 2V and 3V. It is of course to vbe understood that the buses 45, 56,Y 59 and 6I extend to other code determining relays so as to be controlled in accordance with other code jumpers and control levers for other stations 'corresponding to such other code determining relays, only one of which may be'picked up at any one time.

The indication line circuit comprising the line Wires I4 and I 6 is energized from an indication battery IB and has included therein at the control oice, message receiving relays MF and MB which are respectively controlled through front and back contacts of the relays FP and 2F?, as well as through front and back contacts respectively of a dividing relay DV controlled by the relay EP.

A charging resistor CRo is provided for similar purposes, as explained in connection with the resistor CR of Fig. 1.

The indication line Wire I 4 extends to all of the eld stations normally including a back contact, such as back contact |56 of the lock-out relay L01, at each of the field stations.

When a particular iield station is transmitting, the lock-out relay L01 at that station is picked up as Well as the sloW acting repeating relay SA1 with its repeating relay SB1, thereby rendering the open or closed conductive condition of the indication line circuit dependent upon the control of either the relay PF1 or PB1 in accordance with whether the stepping line circuit is energized or deenergized.

The Vpulsing relay PF1 and PB1 are positioned on each step taken by the step-by-step means (including the relays IV1, 2V1, 3V1. LV1 and V131) in accordancewith the station code assigned to that station and indications to be transmitted, such indications being illustrated as Yassociated With a track relay T and a signals-at-stop relay M. The initiation of the system for the trans- 5` mission of indications occurs upon a change in indication conditions by the dropping of a change relay CI-I1 which'is restored after the system is once set into operation.

In the control oice suitable station register- 10 ing relays are controlled by the relays MB and MF of Which the station Vregistering relay 2ST has been indicated. This station registration has been merely indicated, as it is sufficient to understand that a particular station registering relay l5 is picked up corresponding to the station code received. Following the selection of a station relay, the indications are transmitted so that the relays MF and MB control indication registering relays of which relaysIRF 'and IRB have been 2O illustrated as controlled over buses 230 and 233 which may be connected to other indication storing relays by other station registering relays. 'I'he relay IRB is shown as controlling an indicatorrOS through its contact 233.

It is of course to be understood that there is often considerable distance between the central control oice and the outlying field stations, and it is forY those cases in which the distributed capacity in the line circuit is suilciently great to 30 cause troublesome line charging surges that the present system is proposed to be employed.

Although only a part of the whole communication system has beenA disclosed, it is believed that the features of the present invention will 35 be readily understood in connection with the following description ofthe operation, it being understood that the features relative to a communication system of this character have been fully disclosed in the above mentioned applica- 40 tion of Judge etal, Ser. No. 640,062, led October 28, 1932.

Operation of Fig. 2.-Under normal conditions, the line circuits are Vdeenergized and the communication system is at rest. Upon the initia- 45 tion of the system from either the control office or a field station by the actuation of a starting button such as button ISB or by the dropping of a change relay such as relay CHl, a series of impulses of distinctive polarities is placed 50 upon the stepping line circuit to comprise a cycle of operation. The characters of these impulses are determined in accordance with code jumpers and control levers so as to select a particular station and determine the controls for that sta- 5.5 tion, when the system is initiated by the actuation of a starting button such as'button ISB. The code jumper or control lever for each step through suitable circuitmeans picks up either Y the PC relay or the NC relay for that step de- 60 pending upon whether the particular impulse for such step is to be positive or negative in character. Y

For a cycle of operation for the transmission of indications alone, the impulses placed upon the stepping line circuit are all of one character, so that one of the polarity determining relays is picked .up at the beginning of a cycle and is maintained picked up until the end of that cycle. This is accomplished by the picking up of the relay FC through the medium of the indication line circuit upon the dropping or" relay CH1. The indication line circuit includes relay MB by reason of the closed contacts |16 and 206 in multiple with contact I58 of relay 2SA which does not 75 pick up until near the end' of the rst impulse. Closure of front contact |62 of relay MB energizes the pick up circuit for relay FC. The pickingY up of relay FC prevents the relay C from being picked up (by means not shown) so that the bus 58 for the relay NC is continuously energized from (-1-), through back contact 4| ofrelay C and front contact |66 of relay FC.

At the beginning of a cycle of operation, disregarding the type of cycle, one of the polarity determining relays PC or NC is picked up thereby placing an impulse upon the stepping line circuit. This is repeated by the line relays F (with suitable exponents) at the control office and rat each field station as Well as by their respective line repeating relays FP (with suitable exponents). After this impulse has Vbeen applied for a predetermined period of time surfi- -cient for the slow acting relays SA and SB at the control office and at each field station to be picked up, the stepping circuit is opened by the contact 52 of'relay EP. When a suflicient period has elapsed for the time spaceffollowing the first impulse, the back contact of relay EP is again closed.

In brief then, the contacts 5|, 53, and 54 of the relays PC and NC act as pole changing contacts so that particular polarities are placed upon the stepping line circuit from the control battery CB; while theback contact 52 of relay EP is intermittently operated to space the impulses of a cycle. It may be stated in this connection, that the relays PC and NC assume their positions while the back `contact 52 of relay EP ,is open, but remain in static or steady conditions closed.

As previously mentioned, the relay FP in the control oiiice repeats each impulse placed upon the stepping line circuit by reason of circuits closed by the contact 5l, irrespective of the character of energizaticn of the line relay F. Similarly,A each energization of the relay FP is repeated by the relay 2FP by reason of the closure of its front contact 68. Also, the front contact 59 of the relay 2FP ycontrols the relay SA, as previously described. At the iield station, the relay FP1 repeats the line relay F1 by reason of its control by contact ||l|.

During the first part of a cycle, the relaySO1 and the relay SOS1 are selectively picked up and selectively maintained picked up throughout the cycle in accordance with the code so that if the cycle of operation is for the transmission of controls to that station, then the relay S01 remains picked up and causes, through its contact |34, the stepping relays to operate throughout the cycle of operation. If, however, the cycle ofV operation is for the transmission of indications, the relay L01 .has been picked up by the relay CLE-i1 so that contact Ill is closed throughout the cycle of operation causing the stepping operation to continue. Thus, irrespective of whether it is a cycle for the transmission of both controls and indications, a cycle of operation for the transmission of indications alone, or a cycle of operation for the transmission of controls alone, the `stepping relays operate when such station is sending and/or receiving for such cycle. However, the features of the present invention relate more particularly to the indication transmission sc that the operation for the transmission of indications will be considered more particularly.

At the beginning of a cycle following the re- -sponse of the relay SA to the rst impulse which is slightly'longer than the rest, the relay DV is subject to the relay EP. In other words, each time the relay EP is deener'gized to cause lan impulse, the relay DV is energized by reason of a circuit from through front contact |11 of relay SA, back Contact |18 of relay EP, windings of relay DV, to

New assuming that at the beginning of the cycle, the relays L01 and SB1 are picked up so that the field station is conditioned to transmit, then during each time space in the series of impidses, the positive terminal of the indication battery IB is connected to the line wire I4' through the lower Winding of relay MB and the indication circuit ifs dependent for its closed or open conductive condition upon the front contact liti of the relay fPBl. More specifically, assuming the front contact |9| of relay PB1 to be closed, a circuit is completed from the positive terminal of the .indication battery IB, through a circuit including back contact |51 of relay DV, lower Winding of relay MB, b-ack contact 265 `of relay FP, back contact |16 of relay ZFP, line wire |11, front contact |56 of relay L01, front contact |`|2 of relay SB1, back contact |13 of relay FP1, front contact |9| of relay PB1, resistor 2R1, line wire I6, to the negative terminal of the indication battery IB. It is noted that contact |53 of relay 2SA is open throughout the cycle of loperation .after the first impulse, so that the contacts |16 and 206 are entirely effective with respect to the control of relay MB. On the other hand, during each impulse placed upon the stepping line circuit, the indication line circuit is dependent for its closed or open conductive condition upon the'contact |99 of the relay PF1. For example, assuming the contact |99 of relay PF1 to be closed, the indication line circuit is closed from the positive terminal of the indication battery IB, through a circuit including iront contact |57 of relay DV, lower winding of relay MF, front contact |75 of relay FP, front contact |76 of relay 2FP, line wire I4, front contact |56 of relay L01, front contact |12 of relay SB1, front contact |13 of relay FP1, front contact |55 of relay PF1, resistor 2R1, line wire I6, to the negative terminal of the indication battery IB.

In other words, during the time spaces of each series of impulses, the message receiving relay MB is controlled in accordance with the opened or closed condition of the front contact ISI of the relay PE1; but, during the impulses of each series the message receiving relay lVHi1 is controlled in accordance with the opened or closed condition of contact |99 rof relay PF1.

For each time space in aseries of impulses placed upon the stepping line circuit, a step-bystep mechanism at the control oice and at each field station is caused to take one step. Through the medium `of contacts on the step-by-step mechanisrn, the relays PF1 yand PB1 at the field station are caused to be selectively energized in accordance with the positions of devices from which indications are desired in the control oiiice. The relay PF1 is positioned during a time space in accordance vwith the indication it is to transmit on the next impulse period; while the relay PB1 is positioned during ea-ch impulse period in accordance with the indication it is to transmit ori the next time space. Thus, on each step taken by the step-by-step mechanism at a field station, the relays PF1 and PB1 govern the indication line circuit.

Similarly, the message receiving relays MB and MF are effective to control indication storing relays on each step taken by the step-by-step mechanism in the control oice. More specifically, the message receiving relay MB is positioned during each time space marked off on the stepping line circuit in accordance with the position of contact |9| of the relay PB1, for example, and this position is maintained during the following energized period of the stepping circuit so as to suitably position an indication storing relay in accordance with its energized or deenergized condition during such impulse period.

Likewise, the relay MF is positioned in accordance with the position of contact |99 of relay PF1, for example, during each impulse period marked off on the stepping line circuit, and this condition of the relay MF is maintained during the following time space so as to properly position during such time space an indication storing relay. These relays MB and MF control their respective indication storing relays during the proper periods marked off on the stepping line circuit as rendered effective by the step-by-step mechanism at the control office by their contacts 2 I0 and 2|1 which usually apply positive or negative potential depending upon their released or picked up positions to their respective indication storing relays. However, it is believed unnecessary to discuss in detail the operation of the step-by-step mechanisms and the indication storing relays for an understanding of the present invention, as such means has been disclosed in various prior applications, as for example, the application of Judge et al., Ser. No. 640,062, led October 28, 1932, above mentioned.

During the shift from one period to another, that is, from an impulse period to a time space period, or vice versa, there is an interval of time during which the indication line circuit is not energized from the indication battery IB, and during which the distributed capacity of the indication line circuit may become discharged by reason of the closed condition of one of its controlling'contacts at a iield station. This is because the field station apparatus is not permitted to change the condition of the indication line circuit until after the indication line circuit is opened at the control oiiice, which is necessary to provide that the message receiving relays will be properly controlled. Then, the transfer at the field station occurs so that upon the closure of the indication line circuit at the control oiiice, the conductive circuit then established is dependent upon the governing contact at the field. From this it is obvious that a charging current Will flow at the beginning of each period which follows a period during which the indication line circuit has been conductively closed at the field station.

Let us consider the conditions for animpulse period with the relays DV, F, FP, 2FP and FP1 picked up. Then the relay MF is energized or not dependent upon the closed or open condition of the contact |99 of the relay PF1. Let us assume that the contact |99 of the relay PF1 is closed, but the contact |9| of the relay PB1 is open. Thus, the relay MF will be energized and its contact 2|1 will be picked up.

Upon the picking up of the contact 52 of the y relay EP to mark the end of the impulse period, the relay DV is deenergized by the opening of the back contact |18 of the relay DV, so that the indication battery IB is removed from the indication line at substantially the same time that the line relays 'F' (with suitable exponents) assume deenergized positions.

As the contact |51 of the relay DV assumed a dropped away position at substantially the same time that the line relays F assume deenergized positions, then the indication line circuit is deenergized at the control ofiice prior to the shift from contact |99 to the contact |9| at the eld station by the dropping of relay FP1. We have assumed that the contact |99 is closed and that the contact |9| is open. With the source of current supply |B removed from the line circuit, the closed condition of the contact |99 discharges the stored energy in the distributed capacity of the line circuit comprising line wires I4 and I6.

As the relay 2FP repeats the relay'FP, its contact 16 assumes a back point position slightly after the contacts and 206 of the relay FP assume Ytheir back point positions. The release period for the relay 2FP is preferably of sufficient duration to provide for the charging of the distributed capacity, and its contact |16 preferably assumes a dropped away position slightly after the operation of the contact |13 of relay FP1 to a back point position, soe that when the contact |15 assumes its position, the line circuit has been changed and is governed in accordance with the contact |9| of relay PB1.

The charging resistor CR,o provides a circuit from the positive terminal of the battery IB, through the b ack contact |15 of the relay FP and the front contact |16 of the relay 2FP (just before it operates), to the line wire |4 which allows a. charging current to flow to charge the distributed capacity in the transmission line circuit. This charging current charges the distributed capacity of the line to a sucient value prior to `closure of back contact |16, so that the charging surge of current is below the pick-up value of the relay MB upon the closure of back contact |15.

It is readily apparent that similar conditions, as above described, occur during the transition from the time space period on the stepping circuit to an impulse period, but such conditions may be understood by analogy, it being thought sufficient to only point out the charging circuit. When the change is made from the branch including the relay MB and Contact 9| to the branch including relay MF and contact |99, the precharging circuit includes the resistor CRO, front contact 206 of relay FP and back contact |16 of relay 2FP.

In brief, during the transfer from one branch of the line circuit to the other, the distributed capacity of the line circuit may become discharged due to the closed condition of the contact governing the conductive circuit for the first branch, but the distributed capacity for the line circuit is precharged through the charging resistor CR.o before the relay for the second branch is inserted into the circuit to thereby provide that it will be governed in accordance with the conductive condition of that branch and not operated by a surge. In other words, a precharging circuit is completed for charging the distributed capacity of the line circuit whenever the relays FP and 2FP are out of correspondence and just prior to the insertion of a message receiving relay in the line', to thereby prevent or eliminate the maximum current flow of charging current through the line relay, which would result in certain cases in a false indication.

It willbeV apparent from the above description that, after the transfer is made from one branch to another-with the contact governing the conductive circuit' at the eld station for the second branch closed, the indication receiving relay for that branch is energized through a conductive circuit having a normally steady current value sufficiently above the pick-up value for the indication relay for that branch to cause it to assume the energized position.

For example., the relay MF is energized by a circuit closed from the positive terminal of battery IB, through a circuit including front contact |51 of relay DV, lower winding of relay MF,

front contact |15 of relay FP, front contact |16 ofrrelay 2FP, line wire I4, front contact |56 of vrelay L01, front contact |12 of relay BB1, front contact |13 of relay FP1, front contact v|99 of relay PF1, compensating resistor 2R1, return line wire 6, to the negative terminal of the battery IB. Y

Similarly, the relay MB is energized by a circuit closed from the positive terminal of the battery IB, through a circuit including back contact |51 of relay DV,v lower winding of relay MB, back contact 266 of relay FP, back contact |16 of relay ZFP, line wire I4, front contact |56 of relay L'Ol, front contact |12 of relay SBl, back contact |13 of relay FP1, front contact 9| of relay PBl, compensating resistor 2R1, return line wire |6, to the negative terminal of the battery IB.

It may be noted that the compensating resistor 2R1 is of a value consistent with the distance of the field station from the central cnice in comparison with the distanceof the more remote eld stations from the central oice. In other words, the resistance of the indication line circuit is maintained the same irrespective of whether the b ack contact |56 of the relay L01 is closed, allowing some distant station to transmit, or whether front contact |55 of relay L01 is closed allowing the first le'ld station to transmit.

A wire with negligible resistance could be sub'-y stituted for the charging resistor CRO, but it is desirable to use suiiicient resistance to prevent excessive current flow in case there should be a short circuit between line conductors I4 and I6 near the control office and to avoid unnecessarily large current flow if the controlling contacts at the eld location are closed prior to inserting the indication receiving relay. Therefore a value of resistance for resistor CRo is chosen so that the line will be sufciently charged in the desired time and so that excessive current iiow will not take place under the circumstances described above. It is to be understood that the time allotted for charging the line is a matter of design and that it is made long enough to permit the line to be suiilciently well charged before inserting the indication receiving relay.

Discussion of electrical characteristics This discussion of electrical characteristics of the circuits above described is merely for the purpose of making clear the relationship of the charging resistors of the present embodiment of Vthe invention with the operating values of the certain relationships, irrespective of the values which are involved in the application of the present inventio-n, and irrespective of whether the particular values and characteristics of the circuits are determined experimentally or by calculation.

With reference to both Figs. 1 and 2, the system in each case connects the charging resistor CR in series with the transmission line and the value as to be negligible for practical purposes.

It is preferable that the charging resistor shall be maintained inthe circuit to charge the distributed capacity until the charging surge of current has risen to its peak value and then decreased below the pick-up value of the relay to be inserted, which insures that the relay will not respond if` the circuit is not conductively closed at the eld station.

However, it should be noted in this connection that the pick-up value of a relay is usually considered the steady current value and disregards the time which is required to operate its armature from a released position to an actuated or energized position. Thus, a momentary energization of the relay with current of a value slightly above the pick-up value for a time period or" the armature for that particular degree of energization would be ineffective to actuate the relay. In other words, if the surge value of a charging current rises above the pick-up value of a relay but is of insufficient duration to overcome the inertia of the relay, then it is immaterial if such rise above the pick-up value occurs. But, where a transmission line has a fairly large value of distributed capacity, the peak value of the charging surge of current is of such a high v alue and isv existent for such a long period of time, as to usually cause the operation of a line relay employed in connection therewith.

In View of the above, it is apparent that i1- the pick-up current value for a particular relay 1s considered to be its steady current operating value, then it may be possible to insert it into the line circuit slightly before the surge value of the charging current recedes or decreases below such pick-up value. However, it is preferable that the surge value should decrease below the pick-up value before the insertion of the indication detecting relay, so that any superimposed surges, which might be incurred during a transfer from the charging circuit to the relay winding, might not effect an operation of the relay armature.

It is also desirable to insert the indication detecting relay before the charging current has decreased to zeroV or a steady value dependent upon the leakage of the line to minimize the less than that required to overcome the inertia delay. This is especially true in the case of a selector system, as shown in Fig. 2, where such a delay would be multiplied many times by reason of the large number of successive transmitting periods in each cycle.

Also, it should be noted in this connection that under certain conditions line circuits have a leakage current which flows depending upon the insulation of the line circuit. In other words, after the application of a potential to a line circuit having appreciable leakage, a current flows which rises to a peak value and then decreasesV to a steady value dependent upon the leakage of the be well below the pick up value of the indication detecting relay.

The lower the resistance value of the charging resistor in the charging circuit, the more quickly will the desired charged cordition be obtained, but it is desirable to maintain the resistance of the charging resistor substantially equal to the resistance of the corresponding windings of the line relays to be inserted, so that, when a closed conductive circuit exists while the charging resistor isrincluded in the circuit, an excessive current iiow will not occur.

As the resistance value of the charging resistor is raised, the peak value of the charging surge of current is lowered, but the time required for the peak value to recede or decrease below the pick-up value of the relay to be inserted is increased. Therefore, the particular resistance value of the charging resistor is dependent upon the time in which it is desired to charge the distributed capacity before the transfer is made to insert the line relay, and its minimum value is dependent upon the current which is likely to flow under co-nductive circuit conditions if the charging resistor is maintained in the circuit for an appreciable period of time.

General summary From the above description, it will be readily apparent that the present invention provides means in connection with a line circuit having distributed capacity whereby that distributed capacity may be precharged, so to speak, before a relay is included therein to register its constant current conditions. It is, of course, also apparent that the various timing characteristics and sequence of events either in a unit wire system or in a selector system might vary so as to cause the distributed capacity to be discharged at various times and for Various reasons other than those described, but the present invention contemplates that means may be provided in such systems in accordance with the circumstances to be met in such a way that when a message receiving relay is included in the line the operation of this relay will depend upon whether or not the line is closed and will not be operated by unauthorized currents such as occur when a discharged open circuit line is connected to the source of potential.

Although the principles of the present inven`- tion have been applied to embodiments having precharged circuits of the distributed capacity type, it is to be understood that the invention may be applied to circuits having lump capacities or condensers associated therewith without in any way departing from the contemplated scope of the present invention.

Having thus described a communication system with a line circuit arranged in accordance with the present invention, as one specific embodiment of the present invention, it is desired '2,045,908 line circuit. The leakage current obviously mustV distributed capacity, a'source'offenergy, a line relay, means for attimes including said source and said line relay Vin series in said line circuit, and means for precharging the distributed capacity of said line circuit from said source each time before said source and said line relay are included in series in said line circuit.

2. In combination with a line circuit having distributed capacity, a relay, means Veffective to at times insert said relay into the line circuit, and means for pre'charging the distributed capacity of the line circuit each time said relay'is included therein.

3. In combination; two stations; a line circuit connecting said stations and inherently having distributed capacity; a contact at one station for controlling said line circuit .at that station; a relay, a source of current and a compensating resistor at said other station; and means at said other station for at times including said resistor and said relay in series in said line circuit successively in that order, whereby the distributed capacity of said line circuit is charged before said relay is included in said circuit.

4. In combination, a control office, a field station, a line circuit connecting said eld station and control oce and having distributed capacity, a track relay at said field station for opening or closing said line circuit at said field station, a source of current in said control office, a line relay in said control oflice, a compensating resistor in said control cnice, and means Vfor at times inserting successively said compensating resistor and said line relay in that order in series with said source and said line circuit.

5. In combination, a control oiiice, a field station, a line circuit connecting said i-ield station and control office and having distributed capacity, a track relay at said field station for opening or closing said line circuit at said field station, a source of current in said control oiiice, a line relay in said control office, a compensating resistor in said control oflice, means for at times inserting successively said compensating resistor and said line relay in that order in series with said source and said line circuit, whereby said line relay is controlled in accordance with said track relay when inserted in said line circuit, and indicator means controlled by said line relay.

6. In combination, a line circuit distinctively controlled from a remote point during a plurality of successive time intervals, a line relay, a source of current supply, and means at a local point for inserting said source of current supply and said line relay successively in series in said line circuit during certain of said successive time intervals.

7. In'combination, a line circuit kdistinctively controlled from a remote point during a series of measured time intervals, two line relays, means for including said line relays alternately in series in said line circuit during successive time intervals, means forY charging the distributed capacity of said line circuit just prior to the inclusion of each particular one of the line relays in said line circuit, and other means controlled in accordance with the conditions of said line relays during that Ytime interval.

8. In combination, a line circuit, a source of energy, a line relay, means for at times inserting said relay in said line circuit in series with said source, and means for inserting said source in series in said line circuit each time before said line relay is inserted.

9. In combination, a line eircuit having dis- 75,

tributed capacity and at times open circuited and at times closed circuited, a line relay, and means for excluding said line relay from said line circuit when the condition of said line circuit changes but for including said line relay in said line circuit When the condition of said line circuit is stable.

10. In combination with a line circuit having distributed capacity, a source of energy, a line relay, means for at times inserting said source and said line relay in series in said line, means for 'charging the distributed capacity of said line circuit just prior to each time said line relay and said source are inserted in series insaid line circuit and othermeans for controlling the conductive condition of said line circuit to thereby control said line relay.

ll. In combination, a line circuit, means causing said line circuit tobe opened or closed at a remote point, a line relay and a source of energy at a local point, means at said local point .for inserting said source of energy in said line circuit,

and means for adding said line relay in series With said source in said line circuit after said source has been inserted for a short interval of time.

12. In combination, a circuit having capacity included therein, contact means for conductively opening and closing said circuit', a source of energy, control means for at times inserting said source of energy into said circuit, a relay for detecting the open or closed conductive condition of said circuit, and means for adding said relay to said circuit each time said source is inserted, said means delaying momentarily after the operation of said control means, to thereby allow suincient time for the capacity to become charged before said relay is added.

13. In combination, step-by-step means at a k control office and at a eld station operated in synchronism, a line circuit having distributed capacity and connecting the control oflice and field station, means' at the eld station for selectively opening and closing said line circuit on each step of said step-by-step means in accordance with the messages to be transmitted, a message receiving relay at the control oiiice, means inserting said message receiving relay in said line circuit for each step of said step-by-step means, means precharging the distributed capacity of said line circuit prior to each insertion of said message receiving relay, and means in the control oilice distinctively controlled by said message receiving relay on each step of said step-by-step means in accordance with the closed or open 'condition of .said line circuit for` that step as repeated by said message receiving relay.

14. In combination, a stepping line circuit connecting a control office and a field station, means in the control oiiice for impressing time spaced impulses on said stepping circuit, step-by-step means at the control oflice and at the neld station operated in synchronism one step for each impulse on said stepping line circuit, an indication line circuit having distributed capacity and connecting the control oii'ice and iield station, means at the eld station rendered effective on each step of said ,step-by-step. means for selectively opening or closing said indication line circuit for each impulse period and each time space period on said stepping line: circuit for the corresponding step in accordance with messages to be transmitted, two message receiving relays at the control oiiice, means inserting one of said message receiving relays in said indication line circuit during each impulse period on said stepping line circuit, means inserting the other of said message receiving relays in said indication line circuitfor each time space period on said stepping circuit, means precharging the distributed capacity of said line circuit prior to each insertion of each one of said message receiving relays, and means at the control office distinctively controlled by said message receiving relays on each step of said step-by-step means in -accordance with the open and closed condition of said line circuit for each impulse period and each time space period for that station as repeated by said message receiving relays.

WILLIAM D. I-IAILES. 

